1. Field of the Invention:
The present invention relates to the treatment of industrial gases to eliminate recoverable sulfur values therefrom, and, more especially, to the catalytic conversion of such gases (containing hydrogen sulfide, sulfur dioxide and/or such organosulfur compounds as CS2 and COS) utilizing particular cerium oxide-based catalyst.
2. Description of the Prior Art:
The conventional Claus process for, e.g., the recovery of sulfur from gases containing hydrogen sulfide and ofttimes organic sulfur compounds, comprises two stages.
In a first stage, the hydrogen sulfide is burned in the presence of a regulated amount of air to convert a portion of this gas into sulfur dioxide, and, in a second stage, the gaseous mixture thus produced is charged through a series of reactors containing a catalyst, wherein the following reaction takes place: EQU 2H.sub.2 S+SO.sub.2 .fwdarw.3S+2H.sub.2 O (I)
Claus gases may contain, in addition to hydrogen sulfide, carbonaceous sulfur compounds, such as COS and CS.sub.2, which are relatively stable to the conditions of catalytic conversion and which contribute to increased SO.sub.2 emissions, a increase of up to 20 to 50%. Claus gases may also contain those sulfur compounds usually present in the atmosphere following the incineration of flue gases. These toxic compounds are either already contained in the gases to be treated, or are formed therein over the course of the first stage at elevated temperatures.
These compounds may be eliminated according to several types of reactions, in particular, by hydrolysis according to the following reactions (2), (3) and/or (4): EQU CS.sub.2 +.sub.2 H.sub.2 O.fwdarw.CO.sub.2 +2H.sub.2 S (2) EQU CS.sub.2 +H.sub.2 O.fwdarw.COS+H.sub.2 S (3) EQU COS+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2 S (4)
Various catalysts and techniques are known to this art for the catalytic conversion of organic sulfur compounds present in industrial gases.
Thus, alumina has long been employed as a catalyst for this type of reaction. However, alumina displays but mediocre performance relative to the elimination of the aforementioned organosulfur compounds.
Recently, titanium oxide has been used for such catalytic conversion. It displays catalytic activity clearly superior t that of alumina in the elimination of organosulfur compounds. Nonetheless, TiO.sub.2 is characterized by mediocre initial activity for short contact times.